PC817 Photocoupler has a transistor that is controlled based on light (photon). So this IC basically has an IR (infrared) LED and a photo-transistor inside it. When the IR LED has powered the light from it falls on the transistor and it conducts.
PC817 features and specifications
- Input Diode Forward Voltage: 1.25V
- Collector-Emitter Voltage: 80V (max)
- Collector Current: 50mA (max)
- Cut-off frequency: 80 kHz
- Rise Time: 18us
- Fall Time: 18us
- Available as 4-pin DIP through-hole and also as SMT package.
Note: More details can be found at the PC817 datasheet which is available for download.